THE FLORA OF THE COAST ISLANDS. 515 



THE FLORA OF THE COAST ISLANDS OF CALIFORNIA IN RE- 

 LATION TO RECENT CHANGES OF PHYSICAL GEOGRAPHY. 



BY JOSEPH LE CONTE. 



Read September 5, 1887. 



Some of the results reached by Mr. E. L. Greene in his 

 studies of the flora of the islands off the coast of Southern 

 California^ have deeply interested me, because I believe their 

 explanation may be found in geologically recent changes in 

 the physical geography of California. 



These remarkable islands, 8 or 10 in number, are strung 

 along the coast from Point Concepcion southward, and 

 separated from the mainland by a sound 20 — 30 miles wide. 

 They are of considerable size (the largest being about 200 

 square miles in extent), and vary in height from 1,000 to 

 3,000 feet. They have all the characteristics of continental 

 islands, and are undoubtedly outliers of the mainland, at 

 one time connected with it, but now separated by subsidence 

 of the continental margin. They may be regarded as the high- 

 est points of the old coast range outside of the present coast 

 range, the broad valley between the two being now covered 

 with water. Moreover, the date of the separation may be 

 determined with certainty. That they were connected with 

 the mainland during the later Pliocene and early Quaternary 

 is proved by the fact that remains of the mammoth have 

 been found on Santa Rosa, the largest and one of the far- 

 thest off of them. t They ivere, therefore, undouUedly sepa- 

 rated during the Quaternary Period. 



The main points in Mr. Greene's paper with which we are 

 here concerned are the following : 



*Studies in the Botany of California and Parts Adjacent, YI. E. L. 

 Greene. 1— Notes on the Botauj- of Santa Cruz Island. Bull. 7 Cal. Acad. 

 Sci. 



iProc. Cal. Acid, of Sci. vol. V., 152. 



